1. Field of the Invention
The present invention relates to an image forming system, an image processing apparatus, a determination device, and an image processing method. More specifically, the present invention relates to an image forming system, an image processing apparatus, a determination device and an image processing method for performing error-correcting coding of an information source by using an error-correcting code.
2. Description of the Related Art
In response to users' growing awareness of security or for the purpose of improving users' convenience, coded images (such as digital watermark images and two-dimensional barcode images) synthesized with an original image are more frequently printed by using a multifunction printer (MFP). As a two-dimensional barcode image, for example, a QR code is well-known.
In order to ensure that original information can be eventually extracted from a coded image, in practice, an error-correcting code is added to the original information to obtain information with the error-correcting code, and thereafter the information with the error-correcting code is imaged to be the coded image. Note that, in the present specification, “to add an error-correcting code to original information” is referred to as “to perform error-correcting coding.” In addition, “to add an error-correcting code to obtain information with the error-correcting code and thereafter to create an image from the information with the error-correcting code” is referred to as “to create a coded image.”
In this manner, an error-correcting code is added to the original information, so that even if a coded image on a printed material is damaged (for example, stained), the original information can be extracted from the damaged coded image on the printed material.
Here, the description will be given of the error-correcting code by taking as an example a QR code which is one of the standards for two-dimensional barcodes being one example of coded images.
The error-correcting code included in the QR code is a Reed-Solomon code. Regarding the Reed-Solomon code, an error-correcting rate is found by calculating the following formula: (½)×(the information amount of original information)÷(the information amount of the original information+the amount of the error-correcting code). Accordingly, in the Reed-Solomon code, the error-correcting rate is set to 25% when the information amount of original information is equal to the amount of error-correcting code (an error-correcting code amount).
Incidentally, the error-correcting rate of 25% means that the original information can be correctly extracted even if 25% of the QR code is damaged. However, the size of the QR code with the error-correcting rate of 25% is doubled when compared with the size of the QR code with the error-correcting rate of 0% (a coded image without having the error-correcting code added to the original information).
In other words, the original information can be obtained more correctly, even when the QR code is damaged, as the error-correcting rate increases. This is an advantageous feature of the Reed-Solomon code. Meanwhile, a disadvantageous feature thereof is that the size of the QR code becomes larger as the error-correcting rate increases. For this reason, the percentage of the error-correcting code amount is generally determined in consideration of the balance between the above-mentioned advantageous and disadvantageous features.
Regarding the QR code, there are four levels of the error-correcting level as shown in Table 1.
TABLE 1Error-correcting levelError-correcting rateL7%M15%Q25%H30%
Referring to Table 1, the error-correcting level in the above-described example is categorized as level Q.
In addition, it is disclosed in Japanese Patent Laid-Open No. 2004-104494 that a digital watermark is embedded according to a first parameter with regard to resistance of an image and a second parameter with regard to an image quality in order to force the digital watermark to be embedded, when the information amount falls short at the time of the embedding.
According to Japanese Patent Laid-Open No. 2004-104494, when the digital watermark is forced to be embedded, it is determined whether or not all information of the inputted digital watermark is embedded. In a case where all the information is not embedded, the first parameter and/or the second parameter is changed to deteriorate resistance of the image and/or the image quality. With this, when the amount of the information that a user wants to embed is large, all the information can be embedded by reducing at least one of the image quality and the resistance. For example, in a case where the second parameter relates to the error-correcting code amount, the amount of information to be embedded can be increased by reducing this code amount.
When a printer prints a coded image with a high error-correcting rate, the largeness of the coded image printed on a printed material by the printer has been considered as a problem in the conventional cases. To solve this problem, a coded image with a relatively low error-correcting rate is printed by the printer.
However, when the printer prints such a coded image with a low error-correcting rate, there is a problem that original information cannot be extracted from the coded image printed on the printed material by the printer. This often occurs, for example, when the print precision of the printer is low.
It should be noted that, in the present specification, an event in which original information fails to be extracted from the coded image is referred to as an occurrence of an extraction error.